1. Field of the Invention
The present invention relates to a high frequency antenna module having two sets of internal antennas corresponding to the same frequency, which is used in a portable telephone or a wireless LAN. Hereinafter, “High frequency” is in a range from 100 MHz to 20 GHz.
2. Description of the Related Art
Some portable wireless communications apparatus for wireless LAN employ a plurality of antennas in a so-called diversity system. Space diversity, pattern diversity, polarization diversity, frequency diversity, and time diversity are examples of the diversity system.
Among others, the space diversity system uses two or more antennas for reception, which are physically separated from each other. Though there is no need for the plurality of antennas, if one antenna is able to transmit and receive electromagnetic wave in all directions, the plurality of antennas are practically mounted. As the antenna in the diversity system of this type, a chip antenna having the radiation electrodes formed on the surface or inside of a base substance is typically employed (refer to patent documents 1, 2 and 3). As the scheme for the dielectric chip antenna, a monopole, an inverted F, and a patch are known. Since the high frequency module built in the portable unit for wireless LAN is strongly required to be smaller, the antenna is also required to be miniaturized. Consequently, the dielectric chip antenna is mounted on a printed board. An antenna module in which a plurality of chip antennas is arranged on the mounting substrate has been known (refer to patent document 4).                [Patent document 1] JP-A-2000-13126        [Patent document 2] JP-A-9-55618        [Patent document 3] JP-A-10-98322        [Patent document 4] JP-A-9-199939        
The antenna modules using such chip antenna is satisfactory from a viewpoint of miniaturization for the portable or wireless uses, but does not necessarily meet the antenna characteristics such as the reflection coefficient and the radiation gain. The present inventors have made elaborate researches on the antenna characteristics, which greatly depend on the arrangement and positional relation of two antennas, when two antennas are mounted on one end face of the mounting substrate. Consequently the present inventors have found the optimal arrangement and positional relation of antennas to attain the excellent antenna characteristics.